PEEFACE. 



IN writing this book about Crayfishes it has not 

 been my intention to compose a zoological mono- 

 graph on that group of animals. Such a work, to 

 be worthy of the name, would require the devotion 

 of years of patient study to a mass of materials 

 collected from many parts of the world. Nor has 

 it been my ambition to write a treatise upon 

 our English crayfish, which should in any way pro- 

 voke comparison with the memorable labours of 

 Lyonet, Bojanus, or Strauss Durckheim, upon the 

 willow caterpillar, the tortoise, and the cockchafer. 

 What I have had in view is a much humbler, though 

 perhaps, in the present state of science, not less use- 

 ful object. I have desired, in fact, to show how 

 the careful study of one of the commonest and most 

 insignificant of animals, leads us, step by step, from 

 every-day knowledge to the widest generalizations 



